The object is to exploit Gallus domesticus as a vehicle to broaden knowledge of immunogenetics. Avian studies should not only aid in the construction of the evolutionary history of the major histocompatibility complex (MHC) but, more importantly, may lead to greater insight into the functional relationships between the MHC-linked loci and cell-cell interactions. Focus will be on the chicken MHC with special reference to disease resistance. Specific aims are (1) characterize MHC cell surface antigens both genetically and biochemically, (2) relate MHC structure to function, (3) search for MHC gene markers controlling complement activity using monoclonal antibodies, (4) relate specific subregions of the MHC to economically important traits, (5) test for MHC subregion control of disease resistance by challenge with pathogens, (6) relate basal levels of immunoglobulins controlled by MHC to disease resistance, (7) search for MHC-related complementation of immune response genes, (8) try human hemoglobin and egg white lysozymes as a substitute for the amino acid polymer, GAT, currently used to mark the immune response region of the MHC, and (9) produce new, useful recombinant MHC heplotypes. Procedures will include (1) special methods to serotype for B-G, B-F, and B-L gene markers of the MHC, (2) in vitro chorioallantoic tests for susceptibility/resistance to avian tumor virus (ATV) challenge, (3) live bird tests for ATV challenge, (4) monoclonal antibody preparations to identify Ia-like antigens and complement, and (5) assay of virus neutralization activity using embryo fibrablast cell cultures. To identify and isolate cell-surface protein molecules, procedures will include immunofluorescence, ELISA (enzyme linked immunosorbent assay), radioimmunoassay, radial immune diffusion, affinity chromatography, electrophoresis and isoelectric focusing. Purification of complement components, lysozyme, and hemoglobin will be accomplished by column chromatography and gel electrophoresis.